Re: EDM home brew units ?

>
> I figured that out, but since we started the discussion by talking
> Langolis, And the gentleman who wanted a power formula was using a
> Langoiks type circuit, I assumed you were also talking an R/C

circuit.

Sorry I thought I also gave the amount of energy discharged in an RC
circuit, I meant to. I was trying to show the difference.

> Pogo graphite offers the formulas for thier products in so many

amps

> per square inch. I assume that different machines use different
> technology and each has it's own formulas.
>

Can you post a link, it would be handy to know what the equations
actually relate to.

> But, since there is no public schematic that discusses that type of
> circuit the two worlds do not directly relate.

I don't see why, just because you can't buy a book on ebay on how to
build such a machine does not put it out of anyones reach, we don't
put boarders like this on other cnc topics. There are plenty of
other more technical books on general machining that explain the
basics of all kinds of relaxation and forced oscillator edms.

Try http://print.google.com

you can search for books and then search in the books.

> But that would also mean that either the unit is continuous
>sparking
> and not in a pulse type circuit or that the spark voltage goes
>from a working voltage to zero when the cuircuit is open.

the unit it not contiuous sparking because there is no voltage
across the gap when the transisters are off.

OK, in an RC circuit the voltage rises to some level at which point
it sparks and the C is discharged. The point at which this happens
is a function of the gap resistance which you control with the servo.

With a switched circuit you wham on say 100v by switching on the
transister(s) after a short delay the gap ionizes (because it takes
time) and current starts to flow. The voltage seen across the gap
is a function of the limiting resister value, the gap resistance and
the gap voltage. Now just as you say a high current will tend to
lower the gap voltage where as a O/C will mean you see the supply
voltage across the gap and no current flows What you want is to
alter the gap resistance using your servo system such that you see
the average gap voltage that you want. This may be say 50% of the
supply voltage or something. The servo system cannot ajust the gap
pulse by pulse but the good, bad and ugly pulses producing medium
high and low gap voltages can be averaged out and compared to a
reference.

There are also more complex ways of monitoring the gap conditions
such as counting the relative numbers of good sparks, arcs and OCs.
Other methods involve timing how long it takes for the gap to brake
down, short time = arc, long time = OC

between RC and pulser there are loads of circuits, many to avoid
patents it seems. More recently it looks like inverter current
sources are used, these force their working current if they can
whamming really high voltages on the gap until it brakes down and
then reducing it once the "channel" is open. Again the gap voltage
is a function of gap resistance v = IR so can be used for feedback.

> Can you elaborate a little more on the type of circuit you are

talking

I hope I have

Graham